ROPS have been used to protect tractor drivers from crushing injuries caused during tractor roll over accidents. A common type of ROPS used consists of an inverted U-shaped bar having two uprights joined at their upper ends by a crossmember and fixed to a pair of brackets at their lower ends. The brackets are either attached to existing holes in the rear axle or with the use of clamp plates and bolts, are clamped around the rear axle housing. Bolts are then passed through the apertures and into the existing holes or passed through the lower clamp plate so as to fasten the brackets to the rear axle housing of the tractor and thereby mount the ROPS onto the tractor for use.
This type of ROPS arrangement suffers in that it may only fit tractors of a specific model, whereas tractors come in a large range of models. Thus it may be difficult and expensive for tractor owners to find and ascertain ROPS which correctly fit their tractors, and for ROPS manufacturers to produce a large variety of sizes and models of ROPS required to accommodate the differing nature of the tractors.
The large range of ROPS required, along with the size and shape of this type of ROPS, can also be problematic during transportation thereby leading to increased freighting costs. Furthermore, the process of drilling holes in the rear axle can be inefficient and improperly performed.
Thus there is a need for a ROPS which can be mounted on to a variety of tractors of differing models and sizes. There is also a need for a ROPS which can be efficiently freighted.
Drivers of standard size tractors are able to fit a ROPS for a large range of tractors. This market is well developed and many models can be purchased with original equipment or retrofitted equipment. Australian and international standards exist for such bars.
Operators of hobby farms and market gardens prefer small scale tractors with a mass 400-2000 kg. These have a differential housing at the rear wheels and the housing incorporates the three point lift linkage for supporting implements.
Additionally the housing has threaded bores for the reception of attachment bolts to permit the use of specialised equipment. Several brands of compact tractors are popular and each brand includes a variety of models. The existence of prevailing standards means that if an owner wishes to comply ROPS with the law, each model must have an individually designed ROPS.
The ROPS comprises a hoop and a fabricated bracket which connects the hoop to the tractor such that upon roll over the hoop ensures that there is clearance between the tractor and the ground thereby reducing the risk of crushing injury. The ROPS must be carefully designed and tested to ensure adequate energy absorption is achieved, without excessive deflection, in compliance with the relevant standards. The bores in the bracket must register with the threaded bores in the housing and the parts of the bracket must not impede the movement of the links of the three point linkage.
The cost of safety equipment is unwelcome to operators. The costs incurred by manufacturers in the design of the variety of individual components and the costs to dealers who would have to stock the variety of components would generate prices which would be a barrier to the adoption of the roll protection bars on small tractors.
Operators do not want components which are heavy to lift and difficult to fit. The drivers require a component which will withstand the force of roll over but which will not impose loads which would damage the housing to which the component is bolted.